AuthorTopic: The Question of 2-2-V-1 (Read 554250 times)

Ric sez "...We need to document when #3 rivets stopped being used for primary structure. "

Maybe I missed something, but why should we think it's part of the "primary structure"? The thin aluminum, use of small rivets, and lack of cross bracing would seem to me to indicate that it was not structural, but rather a simple skin covering a non-structural area, like the lavatory window proposal, or maybe a temporary field repair of some other aircraft using what was at hand.

When I've drilled out say a 1/8 inch rivet from an existing structure I am directed to re drill the empty hole with a somewhat larger drill i.e. drill out w/#40 drill and redrill w/#42 and then put in an "oversized" 1/8 rivet.

Has this practice changed over the years?

Would this account for the differance in a #3 rivet nominal dia. and the hole size in 2-2-V-1 of 5/32in.?

When I've drilled out say a 1/8 inch rivet from an existing structure I am directed to re drill the empty hole with a somewhat larger drill i.e. drill out w/#40 drill and redrill w/#42 and then put in an "oversized" 1/8 rivet.

Has this practice changed over the years?

The practice I've always known and followed was to use care in drilling only deeply enough to 'pop' the head of the rivet off, then 'punch' the shank and remaining tail ('buck' tail) out of the hole, leaving hopefully a nearly pristine hole at its original size.

This works well much of the time when the mechanic is experienced and the original hole is good. I've probably drilled a million heads off without touching the base metal - drill down through the 'dimple' nice and straight (you learn to compensate for bit drift quickly and keep it centered when drilling lots of these), then 'pop' the head off with a flick of the bit at the end by 'leaning' the drill slightly; if you drill true, this works like clock work. Then come behind with an awl and hammer and rap the tails (shank and tail) out of the hole with a sharp blow (not like driving a spike - just a light but sharp rap).

That said, sheetmetal, like the world, isn't perfect - so frequently one cannot readily punch the shank out and must drill part way - or sometimes all the way, through the sheets to remove it. That happens typically where the original hole was somewhat large and irregular to start with. When that happens, one often is stuck going to the 'next size' - which in the case of the 3/32" rivet ("#3") would mean a 1/8" rivet ("#4"), not two sizes up (5/32" or "#5"). Driven rivets are nice in that they can cover a multitude of mild sins in terms of slightly egged and tapered holes - but that should not be over-done or you lose strength. A perfect hole is desired, of course and it is better to 'true' the hole next size up.

Quote

Would this account for the differance in a #3 rivet nominal dia. and the hole size in 2-2-V-1 of 5/32in.?

Ted Campbell

I would expect a 5/32" rivet to be a typical replacement for a #4. To see an entire row of #5 rivets suggests they are original - not surprising to see where a keel beam or stringer is concerned, but I don't know the L10 structure that intimately. At the very least I would have thought of the keel-skin rivets being at least 1/8" (#4), not #3 - but what do I know about what Lockheed was doing in 1937 without drawings in-hand. I would have thought it more likely to find original #5 rivets there, actually - which would be consistent with the guidance I quoted up-string here (and linked to AC 65-15).

The rivets I can see on the sides of the bird in lots of photographs (some very clear) appear to my mechanic's eye to be typically #4 by and large, with some larger #5's in areas of concentrated stress, e.g. heavy stringers, gusseted bulkhead intersections, etc. That is more typical. That the belly would have smaller rivets is odd to me because it is an area that is in tension for not only flight, but ground ops - that belly keel absorbs a fair bit of tension (with the skins) as fuselage bending moments occur during taxi, loading, etc. Meaning only that I'm surprised that the belly would have smaller rivets - but again, what do I know about Lockheed's practices of the day, and I'm going by my eyeball estimate of what I see in the photos and am not laying hands on to see up close.

In any case, this artifact is all the more peculiar to me in that it has these light rivet holes - but if that is what Lockheed did on the original structure, then no surprise I guess. I wish we had the drawings of that area.

It could have been used anywhere but Alclad was developed for aviation applications, and that we have a surviving AD rivet (aviation type) in this panel underscores that it was not likely adapted elsewhere in this instance. Everything I can see about this panel says "aviation" - the metal type, configuration and fasteners that were used.

This is the belly of c/n 1052 in the subject area. As far as we know this is original construction. I believe these are all #3 rivets but I can verify that when I'm at there New England Air Museum on February 16.

This is the belly of c/n 1052 in the subject area. As far as we know this is original construction. I believe these are all #3 rivets but I can verify that when I'm at there New England Air Museum on February 16.

Bingo - that picture is worth a thousand trips to the museum -

I just scaled this photo to real size (based on the stations distance for reference) and unless the light is really wreaking havoc I get an actual rivet-head size of about .18" (diameter across the head) - which corresponds to a normal head diameter of approximately twice that of the shank, so it corresponds to the expected .093 size of a 3/32" (#3) rivet.

Whatever you see when you get there will be great to know, but I'm now 99% certain we are seeing stock #3 rivets in the belly of an L10 Electra. I would have bet against it but this is clear evidence - too small to be 1/8" (#4) braziers by my actual scale measurement. I'd sure love to be there and see that bird with you for a first-hand look.

My thought is that it is quite possible that this scrap of aluminum could be the rag-tag end of repairs done to the Lockheed at Burbank (conjecture: can envision trying to finish up last of details to get bird off saw horses, no jig available) - perhaps a quick, light-guage covering over a bent / scratched parent element (skin) that was left in place - it happens in 'real world'. Why? When you are compromised (no jigs / fixtures, just saw horses) you remove as little as possible - if the damage is superficial you might leave in-place, then reinforce; lighter-guage skin applied just adds 'insurance' and covers the 'ugly' - and is easier to contour in.

I admit this is conjecture - but this is a very compelling artifact in my mind. Such a repair also might have been done at some point on the trip later, but probably not likely since we don't know of that. Dings happen, and if obvious, a decision might have been made to apply a temporary scab over a creased or scraped skin until more could be done later. There are all kinds of reasons this piece fits this sort of repair on an L10 or other make and model; what is extremely compelling to me however is how closely it matches a known section of damaged skin on Earhart's Electra, and the relative scarcity of such host / donor aircraft in that part of the world so far as we have been able to determine. Now I am at ease with the #3 rivets, which have been a put-off to me for some time as to what this might have been.

It's to bad that DNA testing couldn't be used to match the artifact to the person that wrote up the work performed or the AI that signed off on the repair. That would definitely put it in the "smoking gun" or even in the "any idiot artifact" category! Yeah I know, "get back to us when you have something productive to add"

Ric...Several days ago Richie made the comment on this artifact in regards to indoor and outdoor temperature of the plane. Having said that...I was wondering with you and others expertise...what would happen in this scenario...Amelia and Fred land the plane. Sits there on the reef for several days in excruciating heat...Interior heats up over 100 degrees while the skin of the plane is unbearable to touch....Within days or hours the plane gets washed out over the edge of the reef...Someone made a comment about the rivets being popped out by pressure as the plane descended into the atolls of the reef. My question is...with intense interior and exterior heat of the plane...What would happen to the insides of the plane when it fills up with cold sea water at those kind of temperatures of the plane? Do the rivets get blown off by the popping of the metal or do they just sit there? I would buy the scenario of rivets rusting off, but at the same time you would see rust or some form of corrosion developing on these rivet holes. Let me know what you guys think...thanks!!!!

This is the belly of c/n 1052 in the subject area. As far as we know this is original construction. I believe these are all #3 rivets but I can verify that when I'm at there New England Air Museum on February 16.

To elaborate a bit more - those do appear to be #3 rivets by physical comparison to a similar rivet and a bit of research into brazier head rivets.

Just did a visual comparison of the rivets in the picture Ric posted but had to use modern AN 470 'universal head' rivets that I had in-hand, my working assumption being that the head diameters were similar. In fact the pictured rivets do more closely match the #3 universal head size, not #4 (meaning they are apparently 3/32" rivets as believed.

Not quite comfortable with my memory on how the 470 compares to the 455 brazier, I checked on line. Per one spec at "Jay-Cee Sales & Rivet, Inc.", the common AN 455 brazier head rivet of old had a slightly larger diameter head for the same size rivet than does the universal ("mushroom" per Jay-Cee: a standard brazier head diameter = shank diameter x2.5.

There is also a modified brazier with a significantly smaller head relative to shank size, and it is possible that we're seeing #4 'modified brazier' rivets with the smaller head size. If we could see the buck tail more would be evident about shank diameter - a #4 has a noticeably larger tail than does a #3 rivet.

I don't doubt these being #3 rivets, I think it is only an outside chance that we're seeing modified (small head) #4 braziers, but short of having Lockheed's drawings and to be thorough it would be good to get a shot of the tails if at all possible to be sure. Of course they are now buried under the floor in the museum bird, but perhaps they have some shots taken during restoration?

I don't doubt these being #3 rivets, I think it is only an outside chance that we're seeing modified (small head) #4 braziers, but short of having Lockheed's drawings and to be thorough it would be good to get a shot of the tails if at all possible to be sure. Of course they are now buried under the floor in the museum bird, but perhaps they have some shots taken during restoration?

You want buck tails? Here's yer buck tails (complete with scale).

We took lots of photos of the interior while the plane was under restoration before they re-installed the floor.

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